DOC: show failing string on numeric parse (#13773)

Author: chris-b1

pandas/src/inference.pyx

@@ -686,9 +686,9 @@ def maybe_convert_numeric(object[:] values, set na_values,
                             raise ValueError('integer out of range')
                     else:
                         seen_float = True
-            except:
+            except (TypeError, ValueError) as e:
                 if not coerce_numeric:
-                    raise
+                    raise type(e)(str(e) + ' at position {}'.format(i))
 
                 floats[i] = nan
                 seen_float = True

pandas/src/parse_helper.h

@@ -66,7 +66,7 @@ int floatify(PyObject* str, double *result, int *maybe_int) {
     return 0;
 
 parsingerror:
-    PyErr_SetString(PyExc_ValueError, "Unable to parse string");
+    PyErr_Format(PyExc_ValueError, "Unable to parse string \"%s\"", data);
     Py_XDECREF(tmp);
     return -1;
 

pandas/tools/tests/test_util.py

@@ -120,7 +120,8 @@ def test_series_numeric(self):
 
     def test_error(self):
         s = pd.Series([1, -3.14, 'apple'])
-        with tm.assertRaises(ValueError):
+        msg = 'Unable to parse string "apple" at position 2'
+        with tm.assertRaisesRegexp(ValueError, msg):
             to_numeric(s, errors='raise')
 
         res = to_numeric(s, errors='ignore')
@@ -131,9 +132,15 @@ def test_error(self):
         expected = pd.Series([1, -3.14, np.nan])
         tm.assert_series_equal(res, expected)
 
+        s = pd.Series(['orange', 1, -3.14, 'apple'])
+        msg = 'Unable to parse string "orange" at position 0'
+        with tm.assertRaisesRegexp(ValueError, msg):
+            to_numeric(s, errors='raise')
+
     def test_error_seen_bool(self):
         s = pd.Series([True, False, 'apple'])
-        with tm.assertRaises(ValueError):
+        msg = 'Unable to parse string "apple" at position 2'
+        with tm.assertRaisesRegexp(ValueError, msg):
             to_numeric(s, errors='raise')
 
         res = to_numeric(s, errors='ignore')